"a body that is submerged into a fluid, loses exactly the same amount of weight, as the weight of the displaced fluid".

This means that a big heavy hollow boat loses a lot of weight when it is in the sea. What a submarine can do is change the amount of water it displaces. This is done by having a ballast tank which can be filled by water or air. Pressurized air is contained in another tank in the submarine.

Actually bigmouth_strikes, there is one important
thing you left out. I'm no expert, so I will screw
up all the terminology.

I believe that
the ballast is less important to the climbing and
diving than motion and the "wings" or whatever they
call the fins that stick out of the top conn
tower and the ones in the back. Basically the
submarine is a lot more like an airplane than like
is a diving chamber. As it moves through the water,
the fins/wings generate lift, just as an airplane's wings
do. Since water is much more dense than air
(about 826 times under normal circumstances), you
only need itty-bitty wings to generate lift.

Thus, a submarine which is zooming around underwater
and suddenly loses power is only a little bit less
screwed than an airplane. They do have compressed
air which they can use for an emergency surface
maneuver, but from what I gather, this is not a
pleasant thing.

Also The Custodian, something may have positive buoyancy at the surface,
but still sink at lower depths. Net buoyancy is a function of water
pressure; at lower depths, the increased pressure will overwhelm
the buoyancy. It's a lot harder to float with 500 feet of water
sitting on top of you than when you're at the surface.
Take the human body. Bodies not wearing
cement shoes float under ordinary circumstances. However,
world record holders and seekers for free diving (without air tanks)
pass the point of neutral buoyancy and must actively swim upward, or they
will sink. I read a great article on these guys in The Atlantic
Monthly a few years ago (it looks like it was the May 1997 issue).

I believe bigmouth_strikes is correct on this. The hydroplanes do not generate lift as such, but they are used to alter the aspect of the submarine and to aid it in changing depth, along with the balast tanks. As far as I can remember, what the submarine will usually do is make itself attain neutral buoyancy, and then use the hydroplanes, very much like an aircraft would use it's elevators, to change the attitude of the sub. This will cause the submarine to go up and down. The ballast tanks can be used on their own though, to make the subsink or rise (therefore making them useful in an emergency; pump lots of gas into the ballast tanks and you're almost certain to rise), whereas the hydroplanes need the submarine to be moving through the water horizonally to operate.

Of these, nuclear power is the most expensive but offers the best endurance. It does, however, add complexity and size to the submarine, and (one would hope) additional costs imposed by stringentsafety procedures. For example, in the U.S. Navy, a nuclear ship always has a reactor crew aboard - even if the ship is already decommissioned and is simply awaiting dismantling.

Diesel-electric subs are a tried and true technology, having seen the world's major navies through two World Wars and over eighty years of use. They are cheap to build and operate. However, submarines powered in this fashion have limited underwater endurance - they must frequently surface (or at least snorkel) to recharge their batteries for electric underwater operation. In addition, the limitations of battery power typically limit underwater performance to a few knots (under 15).

Hydrogen Peroxide Propulsion addresses the underwater endurance issue; since it acts as its own oxidizer, internal combustion engines can be used underwater without having to snorkel. The disdvantages include expensive (relatively) and limited-availability fuel, as well as the dangers of having volatile fuels aboard the boat.

Stirling Cycle engines are one method of avoiding internal combustion engines. All that is required is a heat differential to run them; for example, radioisotope thermal generators (larger versions of those used in space probes) might be used. Or a fuel and oxidizer might be carried aboard for controlled burning.

In any case, there are many options for propulsion; more are being explored as this is written.

One addition to the ballast vs. planes discussion above: for safety's sake, one can 'trim' the boat to to a slight
positive buoyancy with the ballast tanks, and then use a slight downward trim on the hydroplanes to maintain or change depth. The advantage of this approach is that if you for somereason lose your propulsion (which means you may likely have lost the ability to control ballast as well) you can simply wait a bit, and you will float to the surface eventually. Naturally, in combat, under ice or in other particular situations this precaution may do more harm than good.

A submarine is a vessel which has been designed for underwateroperations. It has the capability to operate
underneath the surface or on the surface of the water. This along with it's armament makes it a vital piece to
our nations sea power and sea control.

Evidence of this type of craft goes back into history an estimated 2000 years. Aristotle has described for us
a type of submersible chamber that was used in the year 332 B.C. These were used by the sailors of Alexander The
Great during the blockade of Tiros in order to put obstacles and some types of charges of unknown kind.

In China there had also been a report that a primitive submarine was in existence around 200 B.C. In fact, this
submarine was reported to be able to move by the bottom of the sea.

Later on after many centuries in 1578, a man by the name of William Bornedrafted the first submarine design.
His design included ballast tanks which are used to submerge and surface the craft. Unfortunately his submarine
never got passed the drawing stage.

The first successful submarine was built in 1620 by a Dutchman named Cornelis Drebbel. Cornelis had designed
a wooden submersible vehicle encased in leather. It was able to carry 12 rowers and a total of 20 men. Amazingly
enough, the vessel could dive to the depth of 20 meters and travel 10 km. He conducted several series of trips
below the surface of the Thames River which lasted many hours. This early submarine was the first to address the
problem of oxygen replenishment while submerged.

In 1775 or 1776, an American engineer and student at Yale, David Bushnell invented the Turtle. The Turtle was
egg-shaped and carried only a one man crew. It was driven by two hand-cranked screw propellers, one for forward
movement and the other for versicle movement. The Turtle had a complex system of valves, air vents, and ballast
pumps to control submergence, these were made out of lead and kept the vehicle upright, and it also had a mine
with a time fuse. The mine was supposed to be attached to the bottom of the target ship with a detachable screw.

Piloted by Sgt. Ezra Lee, the Turtle was the first combat submarine. On 6 September 1776 the Turtle attacked the
British flagship HMS Eagle in New York Harbor. When Lee tried to attach the mine to the ship, the screw was deflected
by the ship's copper sheathing. Lee had no other choice but to jettison the mine.

Fulton built a sail for surface runs and a hand-cranked screw propeller for use while submerged. The Nautilus had
a streamlined shape to reduce water resistance and it also had ballast tanks to raise and lower the craft. It also had
diving planes which could be adjusted to determine the vessels angle of ascent of descent. The vessel was 21-24.5 ft
long and carried a crew of 4. The only armament on board the Nautilus was an explosive mechanism called a torpedo.
Basically, it was a box of dynamite.

Some people have stated that the Nautilus could stay under sea for 24 hours at a depth of 8 meters while others
say it could stay submerged only up to 6 hours.

Fulton also was the first to experiment with compressed air for the replenishment of oxygen while under the sea.
However, when he tried to get governmentsupport money he did not receive any so the whole project was dropped.

Later in 1850, Germans constructed the submarine Sea Devil under the supervision of the Barbarian Bauer. This
submarine supposedly made over 130 divings with a large crew of 14.

After the war was over two designers concentrated on the submarines. Simon Lake, who died in 1945, worked out
the idea of submerging by negative buoyancy, which is used today. John Philip Holland experimented in other directions
and won a U.S. Navycontract in the late 1890's. In fact, most of the latter half of the 1800's was used in attempt
to develop an adequate means of submarine propulsion. Both of the inventors experimented with compressed air, steam,
and electricity as power sources.

The French Navy made the most serious and successful efforts in the construction of submarines. The Narval class
submarines were the product of there effort. They were equipped with intergrated systems and mechanisms for autonomous
propulsion and under the sea surface sailing.

Soon after the Narval class submarines were unveiled other big countries joined the "game." Another big factor
in the success of the submarines was the invention of the automobiled torpedo by a fellow named Whittehead in 1870.
This gave the submarine the ultimate weapon.

In 1886 Greece, a naval country, acquired for the first time a submarine. It was the Swiss made Nordenfelt which
was steam powered and could reach speeds up to 9 knots. The Nordenfelt was meters in length and displaced 160 tons.
There was also a torpedo on board for armament. This submarine was in service until 1901.

In 1898 J.P. Holland launched his submarine and it was commissioned the USS Holland. This was the United States
Navy's first submarine. It was 53 feet long and displaced 75 tons. The USS Holland used a gasolineengine while running
on the surface and an electric motor while submerged. At top surface speed, it could reach a speed of 7 knots.

The United States was pushed into World War I partly because of the German's unrestricted submarine warfare. The
Germans were sinking allied ships anywhere and anytime they came upon them. They bombed merchant and passenger ships
killing British and American citizens. The United States noticed that the development of the periscope and self-propelled
torpedo, the submarine became a major factor in naval warfare. The success of the submarines for the Germans led to
the development of depth charges.

The U.S. launched the first of the "S" boats. The boats were 219 ft in length and were considered the first "fleet"
type submarines because for the first time they were able to preform operations with the fleet. The armament of these
boats were torpedoes and deck guns. If it was a small target they would use the deck guns and if it were a large target,
it would get a torpedo.

Between the World Wars there were new improvements in submarine design and operation. Underwater sound devices were
made for communications and for the detection of enemy ships. There also was rescue devices made such as the Momsen lung.
This was a lightweight breathing apparatus used by the crew in case of emergency. The typical U.S. submarine had increased
its speed to 18 knots on a surface run using diesel engines and 8 knots submerged using electric motors. Most of the time
that the submarine would have to surface was to recharge its batteries to continue underwater.

In World War II the Balao class was launched. It had a super thick hull design so it could submerge over 100 feet
more then the previous Gato class submarines. All in all, there were 122 submarines of this class launched making it
the largest class of submarines ever built.

Later on in 1943, the German Navy invented a new piece for their submarines. It was a snorkel mast. This would allow
the submarines to run on diesel power while under water at periscope depth and recharge their batteries. Amazingly enough,
the Germans also came up with an alternative power source in 1944. Hydrogen Peroxide was found to be a good alternative
fuel source for the submarines.

Starting with the Trench class submarines, the Navy removed their deck guns and proceeded to streamline the hull.
They also added the snorkel mast and additional battery power so they could run faster and longer then the previous
submarines.

Although the submarines only accounted for 2% of the U.S. Navy, it proved that the submarines were a needed part
of the Navy. They are credited with the sinking of over 50% of the Japanese naval and merchant fleets.

In 1953 the USS Albacore was launched and commissioned. It had a new hull design which resembled a blimp. The new
hull type proved so successful in providing greater submerged speeds nearly all of the following submarines after it
copied its style.

The USS Nautilus was commissioned in 1954. This was the most technologically advanced submarine of its time. It was
the worlds first nuclear powered submarine. It could reach speeds of more than 20 knots when submerged, and could remain
under water for an indefinite period of time. In fact, in 1958 the USS Nautilus made the first undersea transit
of the North Pole. The development of the Naval nuclear propulsion plant was the work of a team Navy, the government and
contractor engineer who were led by Captain Hyman G. Rickover.

When we entered the year of 1960 the first submarines incorporating a battery of solid-propellent submarine-launched
ballistic missiles with nuclear warheads were built in the U.S. These new weapons were capable of hitting targets about
2500 miles when fired from the submerged submarine.

In 1970 the Ohio class submarines were built with 24 launching tubes for intercontinental ballistic missiles ICBM
each with a range of 4600 miles. The USS Ohio, the first of the class, was commissioned in 1981.

From then to present day, there has been many changes in the submarines. Such changes are those of the technological
advances like the computer of smaller size and more up to date equipment. In our world ever changing, there will always
be something new to replace the old.

Submarines have come a long way from Alexander The Great in 332 B.C. to those in our present day. We have found new
methods of propulsion, air replenishment while underwater, communication, depth control, and armament. Indeed, the submarine
does play a vital role in our history and the continuance of our Navy. Without it, where would we be?

The year was 1620, the city, London. A Dutchman by the name of Cornelius Drebbel began working on one of the first underwater vessels, later to be known as the submarine. Drebbel's sub was basically an underwater rowboat. There were twelve oars which extended through the sides and were sealed with tight-fitting leather flaps. The outer shell was a wooden frame with greased leather stretched around it. Snorkel tubes which were held at the surface of the water by flotation devices provided oxygen.

Between 1620 and 1624, Drebbel actually navigated this vessel, on several occasions, up The Thames River. It was designed to carry multiple passengers, and was propelled by twelve oar men. Drebbel traveled at depths ranging from twelve to fifteen feet deep. Drebbel went on to design and test a number of other vessels. King James I of England actually took a short ride on one of Drebbel's submarines.

A submarine boat; esp., Nav., a submarine torpedo boat; -- called specif. submergible submarine when capable of operating at various depths and of traveling considerable distances under water, and submersible submarine when capable of being only partly submerged, i.e., so that the conning tower, etc., is still above water. The latter type and most of the former type are submerged as desired by regulating the amount of water admitted to the ballast tanks and sink on an even keel; some of the former type effect submersion while under way by means of horizontal rudders, in some cases also with admission of water to the ballast tanks.